Strength Research Of2.5D Braided Composites

2.5D braided composites is a kind of three dimensional (3D) braided composites. Ithas the advantages which three dimensional braided composites have, such as the highspecific modulus, specific strength, resistance of delamination and impact damage etc.2.5D braided composites also overcomes the insufficient in the production of complexstructures of general three-dimensional four-directional and three-dimensionalfive-directional braided composites and so on three multi-dimensional. It shortens theproduction cycle and reduces the cost of production.2.5D braided composites haveabsorbed great attention and been applied widely in aerospace, aviation, shipbuildingand other fields. In this paper, the uniaxial tension, compression and shear strength ofthe warp enhanced2.5D braided composites is studied by experiment and numericalmethods.The first chapter introduces the research background and significance of this paper, aswell as the weaving technology of3D braided composites and molding process. Frommaterial mechanics analysis model, stiffness, strength three aspects of the researchstatus at home and abroad make a summary, and analyses the insufficient of researchstatus, and then the research content of this paper is determined.The second chapter is mainly about the experiment of2.5D braided compositestensile. Through these experiments, the compression and shear mechanical propertiesare researched. The tensile, compression and shear strength values of the2.5D braidedcomposites are obtained. The failure mechanism of the2.5D braided composites isanalyzed by observing to the fracture surfaces.The third Chapter chooses the appropriate fiber bundle cross-sectional area byscanning to2.5D braided composites. Then the representative unit cell volume is builed.After that, cohesion contact is introduced into the fiber-bundle/matrix interface of unitcell finite element model, which is used to consider how the fiber bundle/matrixinterface properties affect those of the material.In chapter four, on the basis of the finite element model, the initial damage criteria areadopted to establish the damage model used to predicate the strength of2.5D braidedcomposites along longitudinal direction. The macroscopic stress-strain curves of thematerial are obtained. Numerical results are compared with experimental data and thereasons of errors are analyzed.